A powder sintered double-layer material and its preparation method

Abstract

The present invention discloses a powder sintered double-layer material and a preparation method thereof, wherein the preparation method comprises the following steps: preparing a surface powder and a base layer powder respectively, wherein the aluminum content in the surface layer powder is 0.01-0.5%, and the aluminum content in the base layer powder is less than the aluminum content in the surface layer powder; filling the surface layer powder into a mold cavity and paving it flat, and filling the base layer powder into a mold cavity already filled with the surface layer powder; obtaining a compact by compression molding; and sintering the compact to obtain an iron-based double-layer sintered material. The present invention can play a role in pore formation by adding aluminum to the surface layer so that aluminum and iron react. The present application uses aluminum to increase the porosity of the iron-based material surface, which can reduce the utilization rate of copper in the material ratio and reduce costs; after sintering, under the premise of the same porosity of the surface material, the deformation of the double-layer material is greatly reduced, which can reduce the amount of mechanical processing of the later material; and at the same time, the specific gravity of the material can be reduced, making the mechanical parts lightweight.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy sintered materials, and in particular relates to a powder sintered double-layer material and a preparation method thereof. Background Art

[0002] As a common metal forming method, powder metallurgy has many advantages. For example, it can be pressed into a final size billet without the need for or minimal use of machining. The metal loss produced by this method is only 1%-5%, while general machining will consume 80% of the metal. Powder metallurgy is particularly suitable for the production of a large number of products with the same shape. It can greatly reduce production costs and save raw materials.

[0003] In order to give full play to the functions of powder metallurgy materials, researchers have designed and developed double-layer powder metallurgy materials. The patent document with application number CN202111552612.8 discloses an iron-based double-layer sintered material and its preparation method, which is mainly achieved by controlling the copper content of the surface powder to be greater than the copper content of the matrix powder. During the sintering process, part of the copper in the surface layer will enter the matrix, so that the surface layer will form a higher porosity and the matrix layer will form a higher density. The expansion coefficient of metals will vary due to their composition, temperature range, etc. According to public data, it is generally believed that the linear expansion coefficient of copper is 17.0μm / (mk), and the linear expansion coefficient of iron is 10-12μm / (mk). Obviously, the expansion coefficient of copper is significantly greater than that of iron. The double-layer material in document CN202111552612.8 has different copper contents in the surface layer and the base. During the sintering process, there is a large difference between the expansion coefficient of copper and the expansion coefficient of iron, resulting in surface deformation of the sintered double-layer material, large deformation, and poor flatness. Summary of the Invention

[0004] The purpose of the present invention is to provide a powder sintered double-layer material and a preparation method thereof, so as to reduce the deformation of the double-layer material during the sintering process.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a powder sintered double-layer material, wherein the double-layer sintered material comprises a base layer and a surface layer, and the method for preparing the double-layer sintered material comprises the following steps:

[0007] (1) Preparing powder: preparing a surface layer powder and a base layer powder respectively, wherein the surface layer powder is an iron-based material and has an aluminum content of 0.01-0.5%; further preferably, the aluminum content in the surface layer powder is 0.1-0.3wt%; the base material is an iron-based material and has an aluminum content of 0-0.01%, and the aluminum content in the base layer powder is less than the aluminum content in the surface layer powder; the surface layer powder and the base layer powder include a lubricant, a binder, and also include one or more of copper, graphite, molybdenum, and nickel.

[0008] (2) Pressing the green compact: The mold is demagnetized before use. First, the surface layer powder is weighed and filled into the mold cavity and flattened. Then, the base layer powder is weighed and filled into the mold cavity already filled with the surface layer powder and flattened. Then, the green compact is prepared by pressing and molding.

[0009] (3) Sintering treatment: The compact is placed in a high-temperature furnace for sintering to obtain an iron-based double-layer sintered material. Preferably, the sintering temperature is 1080°C-1150°C, and the compact is placed with the base layer facing downward and the surface layer facing upward; the heating device is a high-temperature furnace. The high-temperature furnace can be a mesh belt sintering furnace.

[0010] A second object of the present invention is to provide an iron-based double-layer sintered material, produced using the aforementioned method; wherein the surface layer microstructure contains aluminum in an amount of 0.01% to 0.5%. Preferably, the surface layer has a thickness of 1 to 4 mm, specifically 1 mm, 2.5 mm, 3 mm, 4 mm, and the like. Furthermore, preferably, the microstructure of the iron-based double-layer sintered material further comprises one or more of ferrite, austenite, pearlite, martensite, and graphite.

[0011] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0012] Patent document CN202111552612.8 mainly controls the copper content of the surface powder to be greater than the copper content of the base layer powder. During the sintering process, part of the copper in the surface layer will enter the base, so that the surface layer forms a higher porosity and the base layer forms a higher density. However, due to the different copper content of the surface layer and the base, there is a large difference between the expansion coefficient of copper and the expansion coefficient of iron during the sintering process, resulting in the sintered double-layer material having a deformed surface and poor flatness. When making mechanical parts, the processing volume is relatively large, which reduces the utilization rate of the material.

[0013] The present application adds aluminum to the surface material. During the sintering process, aluminum and iron react to form an iron-aluminum compound. During the reaction, the difference in diffusion coefficients between iron and aluminum can play a role in pore formation. When the aluminum content is added more, such as greater than 0.5%, the amount of aluminum that reacts with aluminum is relatively large, the surface material will become loose, and the physical properties of the material will be significantly reduced. The present application uses aluminum components to increase the porosity of the surface of the iron-based material. Compared with CN202111552612.8, it can reduce the use rate of copper in the material ratio and reduce the cost of raw materials. After sintering, under the premise of the same porosity of the surface material, the deformation of the double-layer material is greatly reduced, which can reduce the amount of mechanical processing of the later material. At the same time, it can also reduce the specific gravity of the material and make the mechanical parts lighter.

[0014] In addition, copper is a national strategic material and has always been the preferred variety for warehouse receipt transactions and inventory financing in countries around the world. China is the world's largest producer and consumer of electrolytic copper, but China's copper resources are extremely scarce, with a self-sufficiency rate of less than 30%, and this rate is increasing year by year. The technical solution of this application can reduce the consumption of copper resources and is of great significance.

[0015] Fe-Al compounds include five typical structures: Fe3Al, FeAl, FeAl2, Fe2Al5, and FeAl3. Fe-rich Fe-Al compounds have two ordered structures: B2 and DO3. The density of B2 type FeAl compound is 5.56g / cm 3 The density of DO3 type FeAl compound is 6.72g / cm 3 . In the present application, the Fe content is much greater than the aluminum content, which belongs to the Fe-rich condition. B2 and DO3 are two ordered structures. Table 1 shows the volume corresponding to 1 mol of substance. It can be seen from Table 1 that in the present application, no matter which compound or mixture of the two the sintering reaction product is, the volume of the product is smaller than the sum of the volumes of Fe and Al before the reaction, that is, the same amount of substance reacts, and the volume decreases after the reaction; as the volume decreases, pores will appear inside the material, thereby achieving the purpose of pore formation.

[0016] In the present application, part of the pores in the surface material are due to the reduction in volume after the reaction of Fe and Al. This part of the pores will not cause the expansion of the surface material, that is, it will not increase the deformation of the double-layer material; part of the pores are due to the difference in diffusion coefficients when iron and aluminum react, which causes the expansion of the surface material and increases the deformation of the double-layer material; these two effects interact and superimpose on each other. Through experiments, it is determined that when aluminum components are added, the surface material will expand, which will cause some deformation of the double-layer material.

[0017] Table 1 Density and volume of Fe, Al and their compounds

[0018] Type of substance Amount of substance weight density volume Fe 1 mol 56g <![CDATA[7.86g / cm 3 ]]> <![CDATA[7.123cm 3 ]]> Al 1 mol 27g <![CDATA[2.7g / cm 3 ]]> <![CDATA[10cm 3 ]]> B2 type FeAl compound 1 mol 83g <![CDATA[5.56g / cm 3 ]]> <![CDATA[14.928cm 3 ]]> DO3 type FeAl compound 1 mol 83g <![CDATA[6.72g / cm 3 ]]> <![CDATA[12.51cm 3 ]]> DETAILED DESCRIPTION

[0019] The present invention is described in further detail below with reference to the embodiments.

[0020] Example 1

[0021] (1) Preparation of powder: surface layer powder, the ratio is: 1.5% copper, 0.2% aluminum, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron; base layer powder, the ratio is: 1.5% copper, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron, wherein zinc stearate is a lubricant and spindle oil is a binder.

[0022] (2) Pressing the green compact: The mold is demagnetized before use. First, 10.0 g of surface powder is weighed and filled into the mold cavity and flattened. The mold cavity size Then, 28.0 g of the matrix layer powder was weighed and filled into the mold cavity filled with the surface layer powder, and the mixture was flattened. Then, the compact was prepared by pressing. The density of the compact was controlled to be 6.7 ± 0.05 g / cm 3 ;

[0023] (3) Sintering treatment: The green compact is placed in a high-temperature furnace with the base layer facing downward and the surface layer facing upward; the green compact is sintered at a temperature of 1100°C in a nitrogen-hydrogen atmosphere (hydrogen content 15-18vt%) for 40 minutes to obtain an iron-based double-layer sintered material.

[0024] Example 2

[0025] Compared with Example 1, the difference is:

[0026] The surface powder has the following ratio: 1.5% copper, 0.01% aluminum, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron.

[0027] Example 3

[0028] Compared with Example 1, the difference is:

[0029] The surface layer powder ratio is: 1.5% copper, 0.5% aluminum, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron. The base layer powder ratio is: 1.5% copper, 0.01% aluminum, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron.

[0030] Comparative Example 1

[0031] Compared with Example 1, the difference is:

[0032] The surface powder ratio is: 10% copper, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron.

[0033] Comparative Example 2

[0034] Compared with Example 1, the difference is:

[0035] The surface powder has the following ratios: 1.5% copper, 0.7% aluminum, 0.5% graphite, 0.7% zinc stearate, 0.06% spindle oil, and the balance is iron.

[0036] In this application, 20 samples were prepared at a time for future use in the Examples and Comparative Examples. The samples were then tested. The deformation of the sintered samples was measured using a dial indicator. Specifically, the sample was placed flat on a horizontal workbench with its base layer facing downward. The dial indicator was then fixed to a bracket with the test head pointing vertically downward. The indicator was moved across the surface of the sample to measure the height difference. The highest and lowest points were recorded, and the calculated difference was the deformation. The test results are shown in Table 2.

[0037] The porosity test was conducted according to GB / T 5163. The porosity of the surface layer and the substrate layer was tested. Wire cutting was used to prepare 1.2 mm thin layers on the surface side and the substrate side, respectively. The test results are shown in Table 3.

[0038] This application uses apparent hardness to represent the physical properties of the material. The apparent hardness of the surface material was tested according to GB / T 9097-2016, "Sintered Metal Materials (Excluding Cemented Carbide) - Determination of Apparent Hardness and Microhardness." Each sample was tested at six points and the average value was taken. The test results are shown in Table 4.

[0039] Table 2 Deformation test results of materials in Examples and Comparative Examples (unit: mm)

[0040]

[0041]

[0042] Table 3 Porosity test results of materials in Examples and Comparative Examples (unit: %)

[0043]

[0044] Table 4 Hardness test results of surface materials in Examples and Comparative Examples (Unit: HRB)

[0045] Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Example 1 55.2 54.8 55.3 55.7 55.1 Example 2 56.6 56.0 56.9 56.8 57.1 Example 3 51.5 52.8 52.3 52.1 51.7 Comparative Example 1 54.8 54.3 55.2 54.9 55.0 Comparative Example 2 37.2 39.6 32.5 38.9 30.9

[0046] It can be seen from Table 2 that the deformation amount of Example 1 is significantly smaller than that of Comparative Example 1. It can be seen from Table 3 that, under the condition that the base material is the same, the surface material with a content of 1.5% copper and 0.2% aluminum in Example 1 and the surface material with a content of 10% copper in Comparative Example 1 have the same porosity as the surface material finally obtained.

[0047] As shown in Table 4, for Examples 2, 1, and 3, the surface hardness decreases slightly with increasing aluminum content within the 0.01-0.5% range. The hardness fluctuations between samples within the same Example are also relatively small. When the aluminum content exceeds 0.5%, as in Comparative Example 2, which has an aluminum content of 0.7%, the surface hardness decreases significantly, and the fluctuations between samples also increase significantly. A comparison between Example 1 and Comparative Example 1 shows that, under the same porosity conditions, the hardness of the two samples is not much different.

[0048] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to the embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the embodiments described herein. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a powder sintered double-layer material, wherein the double-layer sintered material comprises a base layer and a surface layer, characterized in that: The preparation method of the powder sintered double-layer material comprises the following steps: (1) preparing powder: preparing a surface layer powder and a base layer powder respectively, wherein the surface layer powder is an iron-based material and has an aluminum content of 0.01-0.5%; the base layer powder is an iron-based material, and the aluminum content of the base layer powder is less than the aluminum content of the surface layer powder; (2) Pressing a green compact: filling the surface layer powder into the mold cavity and flattening it; filling the base layer powder into the mold cavity already filled with the surface layer powder and flattening it; then performing pressing and molding to prepare a green compact; (3) Sintering treatment: The compact is sintered to obtain an iron-based double-layer sintered material; during the sintering process, aluminum and iron react to form an iron-aluminum compound.

2. The method for preparing a powder sintered double-layer material according to claim 1, characterized in that: In step (1), the aluminum content in the surface powder is 0.1 to 0.3 wt%.

3. The method for preparing a powder sintered double-layer material according to claim 1, characterized in that: In step (1), the aluminum content in the base layer powder is 0-0.01%.

4. The method for preparing a powder sintered double-layer material according to claim 1, characterized in that: In step (1), the surface layer powder and the base layer powder both include iron, a lubricant, a binder, and one or more of copper, graphite, molybdenum, and nickel.

5. The method for preparing a powder sintered double-layer material according to claim 4, characterized in that: The lubricant is zinc stearate; the binder is spindle oil.

6. The method for preparing a powder sintered double-layer material according to claim 1, characterized in that: In step (2), the mold is demagnetized before use.

7. The method for preparing a powder sintered double-layer material according to claim 1, characterized in that: In step (3), the sintering temperature is 1080°C-1150°C.

8. A powder sintered double-layer material, characterized by: It is prepared by the preparation method according to any one of claims 1 to 7, and the microstructure of the surface layer contains aluminum element.

9. The powder sintered double-layer material according to claim 8, characterized in that: The thickness of the surface layer is 1-4 mm.

10. The powder sintered double-layer material according to claim 8, characterized in that: The microstructure of the powder sintered double-layer material also includes one or more of ferrite, austenite, pearlite, martensite, and graphite.

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